Alloy process



Patented Oct. 16, 1945 @UNITEDl STATES tion of Delaware vApplicationJanuary 31, 1941, Serial No. 376,918

' s claims. (ci. 75-1305) My invention relates to .the production of aniron-chromium-silicon alloy of low carbon content which is useful as apre-alloy in the production of stainless steel.

Among the objects of my invention are the production of aniron-chromium-silicon pre-alloy of high chromium and silicon contents,in combination .with a low carbon content, in a simple, efllcient,economical and thoroughly practical manner, employing available meltingand furnacing l equipment, and using inexpensive and available,semi-prepared materials or raw materials such as ores, including lowgrade chrome ore when de- "sired, permitting a wide flexibility betweenthe choice of semi-prepared materials. in solid or molten forms, andyielding a-high grade product, with maximum metal per unit of meltingequipyment, and all with a minimum consumption of power and labor, andfull economy of continuous` operation.

Other objects, in part will be obvious and in part pointed'outhereinafter.

' The invention accordingly consistsin the several operational steps,and the relation of each of the same to one or more of the others asdescribed 25 herein, the useful application of which is indicated in theclaims.

In the accompanying drawing, illustrating certain features of myinvention:

Fig. lis a flow sheet for 'the production of ferro- 30 chrome-siliconaccording to one aspect of my-invention; and

Fig. 2 is a ilow sheet of a modified method of producingferro-chrome-silicon according to another aspect of the invention.

As conducive to a clearer understanding of certain features-of myinvention, it may be noted at this point that ierrochrome silicon isfinding use as an inexpensive source of chromium 4in the production ofstainless steel. This is particularly true where it also serves as areducing agent. See for example'the process of producing stainless steeldescribed in the U. S. Letters Patent 1,954,381 issued to me on April10,1934, and entitled Manufacture of rustless iron. Attention also isdirected to the process-'of my co-pending \application for U. S. LettersPatent Serial No. 372,400 filed December 30, 1940,v and entitledProduction of stainless steel.

Ferrochrome-silicon, according to heretofore used practices, commonly isproduced by smelting together chrome ore, quartzite and coke. Anelectric are furnace of the submerged electrode type ordinarily isemployed. I find, however, that this process-is not feasiblecommercially where th Am'rlazlil'r OFFICE Alexander L; fFelld, Towson,Md., assignor to Rustless Iron and Steel Corporation, a corpora`v h tionprohibitive and the production rate so low Q A ing together quantitiesof chrome ore and a caralloy furnace. Secondly I produce ferro-silicon,by smelting together quantities of a carbonaceous pared as above, Icharge them into the Heroult -during the steel furnacing stage, thiscarbon rising great thirst of a chromium steel bath for carbon v, bothare.present in the bath I have discovered chrome ore available is of alow grade. The slagv volume becomes excessive, the power consumpas tomake the process wholly impractical.

Accordingly an object of the present invention is the provision of asimple, elcient and practical process for the 'productionofferrochrome-silicon, using available and inexpensive low grade chromeore, using known and available furnacing equipf ment, all with minimumpower consumption and without encountering unmanageable volumes of slag.Referring now more particularly to the practice of my invention,attention isdirected to Fig. 1 of the drawing. In manufacturing aniron-chromium-silicon pre-alloy in accordance with my invention I melttogether quantities of a chromiumiron pre-alloy and a ferro-silicon. Inaccordance with certain features of my invention, I produce a highcarbon, chromium-iron pre-alloy by smeltbonaeeous reducing agent such ascoke in a ferroreducing agent such ascoke and a high -silica rawmaterial suchvas crushed quartzite in a second ferro-alloy furnace.Desired quantities of the two melts are combined in a steel makingfurnace of the Herault type.

After the ferrochrome and ferrosilicon are pres'teel making furnace insuch quantities that the ratio of available silicon to chromium contentsof the charge ranges between approximately 1/2 to 1 and 2 to l. Carbonis expelled from the mixture to the surface of the melt. 'I'he carbon onthe surface of the melt oxidizes or combines with the slag so that itcanbe subsequently skimmed off. After skimming oi the slag, I tap thefurnace withdrawing molten low carbon ferrochrome-silicon pre-alloy. Thefinal Lproduct is cooled andretained in desired form for future use in.the manufacture. of stainless steel.

In order that my invention may be more clearly understood. it may benoted at this point that the is well recognized in the metallurgy art.VAv chromium-containing steel bath also has athirst for si1icon. Where;however, carbon and silicon that silicon, when present in sufiicientamounts. will cause carbon to be expelled freely from the bath. Theexplanation for this feature may be that once there is sufficientsilicon in thechro- `place the carbon of the ferrochrome.

mium-iron bath to combine with the chromium, carbon' will not bepermitted to do so. Thus, the carbon is expelled from the bath.` I donot, however, wish to be bound by this explanation.

' I ilnd that the ratio of silicon to chromium, necessary 4to expelcarbon and give the desired .low carbon ferrochrome-silicon pre-alloy,ranges between substantially l/2 to 1 and 2 to 1. Silicon to me, causescarbon to be expelled from the bath -as noted above, for some reason notfully known .of metal. Furthenthe amount of carbon exp alloy iscombined, preferably shouldbe high.

In ferro-chrome pre-alloys made from low grade chrome ore, the chromiumpresent of course, will not be sogreat. Consequently, the siliconcontent of the ferrosilicon may be lower, although it will be understoodthat the quantity of ,ferrosilicon necessarymay bel decreased where the`higher silicon material is used.

As a specific example `of the practice of my invention, I convenientlyuse a three-phase ferroalloy furnace, rated 6000 k. v. a. in producingthe ferrochrome. Preferably the furnace is lined with magnesite.Ferrosilicom conveniently is prepared in a like ferrofallpy'furnace,this preferably being lined with carbon brick.. Finally. I prepare suchas to produce directly a ferrochrome-silicon pre-alloy with a maximumcarbon content of 0.2%, approximately 30% to 60% chromium, 60% to 28%silicon and the remainder principally iron.

The relative proportions of the desirable constituents, iron, chromiumand silicon; and the elimination of carbon in my ferrochrome-siliconpre-alloy can, for example/be controlled by analysis'of the rawingredients available for the preparation of ferrochrome pre-alloy andferrosilicon, o r by separate analysis of the ferrochrome pre-alloy andthe ferrosilicon before they are combined, or by analysis of a test heatwhich contains ferrochrome pre-alloy and ferrosilicon in predeterminedproportions. Such trial and error methods when practiced by themetallurgist soon enables him to predict with 'reasonable certainty, thecontent of the final ferrochrcme-sili-y conproduct and also to know theproper amounts offerrochrome pre-alloy and ferrosilicon needed in themelt to produce desired results.

Another somewhat modified method of practicing my" invention isillustrated in Fig. 2 of 'the drawing. Here, as in the method previouslydescribed, I prepare a high carbon, 'ferrochrome pre-alloy by smeltinstogether quantities of low i grade chrome ore and coke in a ferro-alloyfurnace of lthe type previously mentioned. In a second ferro-alloyfurnace, of the type formerly described, I smelt together quantities ofcoke and crushed qurtzite or other silica product. During the smeltingoperations in the two furnaces, molten ferrochrome pre-alloy is tappedin regulated I amounts from the first furnace andis fed over the chargein the second furnace. As a. result the ferrochrome pre-alloy combineswith the ferrosilicon the low carbon ferrochrcme-silcon pre-alloy.v

preferably by combining the ferrochrome prealloy and ferrosilicon in athree-phase Heroult electric-arc furnace rated 3500 k. v. a; To minimizelining attack, this furnace preferably is lined with silica brick,backed up with magnesite. I do not wish, however, to limit my inventionto the-use of any particular type ofy furnace, furnace lining or otherappurtenant structure in any one of the operations disclosed herein.

since it will be readily understood by those skilled.

in the art that considerable latitude of choice exists in the selectionof means to be used in carrying out my invention.

It is to be observed that in the practice of my invention, the chrome`ore charged into the rst of the Vabove mentioned pre-alloy furneceswell may be of a `low grade. In fact my process, as distinguished fromconventional proc as it is producedin the second furnace. Carbonprovides for the production of a low carbon ferrochrome-siliconpre-alloy, in which the silicon and chromium contents are high, usingavailableand inexpensive low grade chrome ores. This is to bedistinguished from the conventional, ex-

esses, is adapted to use such an ore, without en.

countering the unmanageable slag volumes ordinarily met with. The gradeof this ore may be so low as to contain only some^25% to 40% chromicoxide -(01u03) V'I'he ferrochrome; pre-alloy yield usually analyzes 35%to 75% chromium.,with a carbon content-M495 to 8% or more and the re#malnder princlpalb iron. A

The ferrosilicon obtained from the second prealloy furnace,previouslyffmentioned, ordinarily contains a large amount of siliconwhile the remainder thereof is principally iron. Usually ayferro-silicon 'containing at least 40% silicon is required for, asstated above, silicon is largely responsible for the expulsion of carbonfrom the final ferro-chrome-silicon heat. I .prefer lto use ferrosiliconcontaining at least silicon` l In my process, the relative quantities ofhigh carbon ferro-chrome andremo-silicon lused are pensive practice ofsmelting chrome ore, silica and coke to give aferrochrome-siIiconpre-alloy of low carbon content, which practice isnot commercially feasible where low grade chrome ores are employedbecause of the excess slag volumes encountered as noted above.l

While in practicing my invention, I preferably' mix selected proportionsof molten ferrochrome v ferrochrome and solid ferrosilicon. Suchmodi-.f/

fled practices at times are more satisfactory than the practiceofcombining the ingredients strictly in molten form. These modificationsin the methods of carrying out my invention are made so as to have fulleconomy of continuous operation' of the ferro-alloy furnaces with aminimum consumption of power and labor. Any excess ferrochrome orferrcsilicon is 'tapped of! and permated to solidify and e001 afterwhich it is stored for future use.

While certain types of raw materials are des1g` nated, and while certainproportions of iron,

. of my invention, and as many changes mayv be made in the embodimentshereinbefore set forth, it is to be understood that all matter describedherein, or shown in the accompanying drawing, is to be interpreted asillustrative andI not as a limitation.

i I claim: 1. In the production of an iron-chromium-sil con pre-alloycomprising approximately 30% to 60% chromium, 60% to 28% silicon, with amaximum carbon content of .20% andy the remainder principally iron, theart which includes `smelting crushed quartzite and coke with aniron-chromium pre-alloy separately prepared by smelting a low gradechrome ore containing 25% to 40% chromic oxide and comprising 35% to'75% `chromium with a carbon content of 4% to 8% and the remainder iron,the ingredients being in such quantity that the ratio of the availablesilicon to chromium contents of the charge ranges between approximately1/2 to 1 and 2 to 1 whereby carbon is expelled from the melt, andthereafter removing the carbon from the surface of the melt and tappingthe melt free of carbon.

2. In the production of an iron-chromium-silicon pre-alloy of low carboncontent, the art which includes, smelting chrome ore containing 25% to40% chromic oxide with coke in a rst furnace giving'a melt containing atleast 35% chromium and substantial amounts of carbon, smelting quartzitewith coke in a second furnace, charging the melt from the rst furnaceinto the second furnace before or during the smelting operation in suchproportions that the available silicon-to-chromium ratio rangesvbetweenapproximately one-half to one and two to onel whereby carbon is expelledfrom the resultant combined melt, and thereafter tappingV the meltsubstantially free of carbon.

3. In the production of an iron-chromium-silicon pre-alloy comprisingapproximately about y30% to 60% chromium, 60% vto 28% silicon with amaximum carbon vcontent of .20% and the remainder principally iron, theart which includes smelting chrome ore containing from about 25% tochromic oxide with a carbonaceous reducing agent and giving aniron-chromium prethe ratio of the available silicon to ch-romiumvcontents of the charge ranges between approximately 1 /2 to 1 and 2 to1, whereby carbon is expelled from the melt; and tapping the meltsubstantially free of carbon.

ALEXANDER L'.

